This invention relates to a method of battery pack manufacture, and in particular to a battery pack and its method of manufacture wherein batteries and output terminals are inserted into a mold in a process step to form an external plastic case.
A battery pack formed by inserting batteries into a molded plastic resin region, which serves as the external battery pack case, has been developed. This type of battery pack is cited in Japanese Non-examined Patent Publication 2000-315483. As shown in FIG. 1, the printed circuit board 105 and batteries 102 are inserted and fixed in the mold when a molded plastic resin region is formed and becomes the external case of the battery pack. Unlike related art battery packs, this battery pack does not require battery and printed circuit board insertion and assembly in a separately formed case. Here, the printed circuit board and batteries are held in fixed positions during the molding step to form the molded plastic resin region which becomes the case. This type of battery pack can be manufactured inexpensively in quantity.
However, when the battery pack shown in FIG. 1 is actually manufactured in quantity, it has the drawback of poor yield. This is because the molded plastic resin region is difficult to form in a precise configuration. In particular, an error in the printed circuit board 105 dimensions makes molding difficult for a battery pack in which the printed circuit board 105 is inserted into the molded plastic resin region. The printed circuit board 105 is inserted and temporarily held in the mold cavity 111 for molding in the plastic resin region. However, a printed circuit board 105 with error in its dimensions cannot be temporarily held in a precise position in the mold 110. This is because the printed circuit board 105 is slid into, or sandwiched in the mold to temporarily hold it in a fixed position in the mold cavity 111. The mold 110 is designed to allow a printed circuit board 105 with maximum dimensions to be slid or sandwiched in the mold cavity 111 and temporarily held. Consequently, a printed circuit board smaller than maximum dimensions cannot be temporarily held in the proper position, and it also cannot be reliably retained in that position. A printed circuit board which cannot be reliably retained in the mold cavity can easily become further out of position when molten plastic resin is injected into the mold cavity. Therefore, this battery pack has the drawback that the inserted printed circuit board moves out of position. In a battery pack having output terminals attached to a printed circuit board, and having those output terminals exposed outside the molded plastic resin region, there is a further drawback of plastic resin attaching to the surfaces of the output terminals. The cross-sectional view of FIG. 2 shows a mold for forming a plastic resin region that exposes the output terminals outside of the molded plastic resin region. As shown in FIG. 2, it is necessary to tightly contact the mold 210 to the output terminals 203 at the exposed areas. If space is left here, plastic resin can ingress into the gap left between the mold 210 and the output terminals 203 as shown by the broken lines of FIG. 2. This will cover the output terminals 203 with plastic resin. In particular, high manufacturing efficiency injection molding injects molten synthetic resin into the mold cavity 211 at extremely high pressures. Therefore, molten plastic resin can ingress into even small gaps and reduce yield. A battery pack with plastic resin on its output terminals does not allow electrical connection of the output terminals to power supply terminals of an electrical apparatus and is a reject part.
As shown in FIG. 1, a connector 116 provided with output terminals at the end of lead wires 115 is attached to a battery pack having parts such as a printed circuit board which cannot be accurately positioned in the mold. In a battery pack of this configuration, output terminals are not embedded within the molded plastic resin region, and yield can be improved. However, not only does the attachment of lead wires 115 make fabrication more complex, temporary placement within the mold 110 is also troublesome. This is because battery pack parts are temporarily placed in the mold cavity 111 with lead wires 115 pulled outside the mold 110. Furthermore, this battery pack has the drawback that lead wires can be easily open circuited. In addition, electrical equipment which attaches a battery pack having lead wires must provide internal the necessary space to accommodate the lead wires and connector. Therefore, it also has the drawback that space for holding the battery pack becomes greater.
The present invention was developed to eliminate drawbacks of the type mentioned above. Thus it is a primary object of the present invention to provide a battery pack and its method of manufacture wherein output terminals can be inserted in a mold and accurately positioned within the plastic resin mold region.
The above and further objects and features of the invention will more fully be apparent from the following detailed description with accompanying drawings.